scholarly journals Two-dimensional resonators with small openings

1982 ◽  
Vol 24 (1) ◽  
pp. 2-27 ◽  
Author(s):  
G. R. Bigg ◽  
E. O. Tuck
Keyword(s):  
Natural Frequency ◽  
Asymptotic Expansions ◽  
Velocity Potential ◽  
Low Frequency ◽  
Matched Asymptotic Expansions ◽  
Two Dimensional ◽  
Acoustic Response ◽  
Closed Cavity ◽  
Small Opening

AbstractThe acoustic response of a two-dimensional nearly-closed cavity to an excitation through a small opening is examined, using the method of matched asymptotic expansions. The Helmholtz mode of vibration is discussed using a low-frequency expansion of the velocity potential in the cavity interior. The variation in frequency and magnitude of the resonator response is explored, both for the Helmholtz and the natural-frequency modes.

The evolution of stress intensity factors in the propagation of two dimensional cracks

2000 ◽  
Vol 11 (5) ◽  
pp. 453-471 ◽  
Author(s):  
AVNER FRIEDMAN ◽  
BEI HU ◽  
JUAN J. L. VELAZQUEZ
Keyword(s):  
Stress Intensity ◽  
Elastic Medium ◽  
Plane Strain ◽  
Asymptotic Expansions ◽  
Stress Intensity Factors ◽  
Matched Asymptotic Expansions ◽  
Two Dimensional ◽  
Intensity Factors ◽  
Plane Strain Deformation ◽  
Isotropic Elastic Medium

The aim of this paper is to describe a technique based on matched asymptotic expansions that allows us to derive the variation of the stress intensity factors in a homogeneous isotropic elastic medium under plane strain deformation. The case of antiplane shearing is also considered.

Matched asymptotics for two-dimensional planing hydrofoils with spoilers

1998 ◽  
Vol 358 ◽  
pp. 259-281 ◽  
Author(s):  
G. M. FRIDMAN
Keyword(s):  
Asymptotic Solution ◽  
Flat Plate ◽  
Linear Theory ◽  
Asymptotic Expansions ◽  
Flow Problem ◽  
Matched Asymptotic Expansions ◽  
Asymptotic Solutions ◽  
Two Dimensional ◽  
Trailing Edge ◽  
Matched Asymptotics

The purpose of the paper is to demonstrate the effectiveness of the matched asymptotic expansions (MAE) method for the planing flow problem. The matched asymptotics, taking into account the flow nonlinearities in those regions where they are most pronounced (i.e. in the vicinity of the edges), are shown to significantly extend the range where the linear theory gives good results. Two model problems are used: the planing flat plate with a spoiler on the trailing edge and the curved planing foil. Asymptotic solutions obtained by the MAE method are compared with those obtained using linear and exact nonlinear theories. Based on the results, the asymptotic solution to the planing problem under the gravity is proposed.

Fluid Motion Past a Porous Circular Cylinder With Initial Pressure Gradient

1980 ◽  
Vol 47 (3) ◽  
pp. 489-492 ◽  
Author(s):  
J. L. Gupta
Keyword(s):  
Circular Cylinder ◽  
Pressure Gradient ◽  
Drag Force ◽  
Asymptotic Expansions ◽  
Fluid Motion ◽  
Initial Pressure ◽  
Matched Asymptotic Expansions ◽  
Two Dimensional ◽  
Dimensional Flow ◽  
Two Dimensional Flow

The problem of two-dimensional flow, past a porous circular cylinder, with initial pressure gradient is solved using the method of matched asymptotic expansions. It is found that the drag force experienced by the cylinder is increased due to initial gradient although it remains smaller than the drag force experienced by an identical impervious body.

Two-Dimensional Base-Vented Hydrofoils Near a Free Surface: Influence of the Ventilation Number

1975 ◽  
Vol 97 (4) ◽  
pp. 465-473 ◽  
Author(s):  
A. Rowe ◽  
J. M. Michel
Keyword(s):  
Free Surface ◽  
Asymptotic Expansions ◽  
Constant Coefficient ◽  
Cavity Length ◽  
Matched Asymptotic Expansions ◽  
Two Dimensional ◽  
Drag Coefficients ◽  
Lift And Drag ◽  
Limiting Values

The method of matched asymptotic expansions is used to analyze the flow around a base-vented lifting foil with rounded nose beneath a free surface. The foil is defined numerically. Results concerning the lift and drag coefficients and the limiting values of incidences without cavitation are compared with experiments. The relation between the cavity length and the ventilation number at several depths of submergence is given in the case of a symmetrical wedge: it agrees with the experimental one except by a nearly constant coefficient.

Despeckling of Sar Images Using Shrinkage of Two-Dimensional Discrete Orthonormal S-Transform

2020 ◽  
pp. 2150023
Author(s):  
Priya R. Kamath ◽  
Kedarnath Senapati ◽  
P. Jidesh
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Relevant Information ◽  
Detection Algorithm ◽  
Two Dimensional ◽  
Sar Images ◽  
S Transform ◽  
Processing Step ◽  
Frequency Components ◽  
Shock Filter

Speckles are inherent to SAR. They hide and undermine several relevant information contained in the SAR images. In this paper, a despeckling algorithm using the shrinkage of two-dimensional discrete orthonormal S-transform (2D-DOST) coefficients in the transform domain along with shock filter is proposed. Also, an attempt has been made as a post-processing step to preserve the edges and other details while removing the speckle. The proposed strategy involves decomposing the SAR image into low and high-frequency components and processing them separately. A shock filter is used to smooth out the small variations in low-frequency components, and the high-frequency components are treated with a shrinkage of 2D-DOST coefficients. The edges, for enhancement, are detected using a ratio-based edge detection algorithm. The proposed method is tested, verified, and compared with some well-known models on C-band and X-band SAR images. A detailed experimental analysis is illustrated.

scholarly journals Tunable characteristics of low-frequency bandgaps in two-dimensional multivibrator phononic crystal plates under prestrain

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Hai-Fei Zhu ◽  
Xiao-Wei Sun ◽  
Ting Song ◽  
Xiao-Dong Wen ◽  
Xi-Xuan Liu ◽  
...  
Keyword(s):  
Phononic Crystal ◽  
Real Life ◽  
Low Frequency ◽  
Acoustic Vibration ◽  
Crystal Plate ◽  
Frequency Noise ◽  
Two Dimensional ◽  
The Matrix ◽  
Noise Frequency ◽  
Realtime Control

AbstractIn view of the influence of variability of low-frequency noise frequency on noise prevention in real life, we present a novel two-dimensional tunable phononic crystal plate which is consisted of lead columns deposited in a silicone rubber plate with periodic holes and calculate its bandgap characteristics by finite element method. The low-frequency bandgap mechanism of the designed model is discussed simultaneously. Accordingly, the influence of geometric parameters of the phononic crystal plate on the bandgap characteristics is analyzed and the bandgap adjustability under prestretch strain is further studied. Results show that the new designed phononic crystal plate has lower bandgap starting frequency and wider bandwidth than the traditional single-sided structure, which is due to the coupling between the resonance mode of the scatterer and the long traveling wave in the matrix with the introduction of periodic holes. Applying prestretch strain to the matrix can realize active realtime control of low-frequency bandgap under slight deformation and broaden the low-frequency bandgap, which can be explained as the multiple bands tend to be flattened due to the localization degree of unit cell vibration increases with the rise of prestrain. The presented structure improves the realtime adjustability of sound isolation and vibration reduction frequency for phononic crystal in complex acoustic vibration environments.

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